Heating and cooling systems for a plug in type electric vehicle, either a pure electrical vehicle or plug in type hybrid, typically use a vapor compression type heating and cooling system (heat pump) with an electrically driven compressor. This represents a significant electrical load on the system that can shorten the driving range, especially during extremes of ambient temperature, hot or cold.
With internal combustion vehicles, it has been known for some time to use a reservoir of phase change material (“PCM”) incorporated into the evaporator to store the “extra cold” available when the engine driven compressor is running above basic cooling requirements, and to use that during periods of engine shut off (stop lights). Likewise, with internal combustion, there is often “extra heat” from the engine cooling system that can be stored in a PCM “heat battery.” Since, in each case, the stored heat or “cold” is used within the vehicle by direct conduction or convection to the cabin air, the storage temperature, and melt temperature of the PCM material, has to be close to the particular cold or hot comfort temperature that it is desired to maintain, and a single PCM material obviously can only have a single melt temperature. Of course, with an electric, battery driven compressor, there is no “extra” heat or cold available during operation of the vehicle to be stored during vehicle operation, and operation of the compressor at any time during regular vehicle operation is a straight drain of the system that shortens driving range.
One approach to extending driving range has been to charge a PCM energy battery, one storing heat, or one storing cold, while the vehicle is plugged in during a stationary charging event, and to use it, at least temporarily, after the vehicle is started, to reduce the load on the HVAC system, completely for short trips, or at least until the reservoir is depleted during a longer trip. See US20120152511. There, it is proposed to use a separate thermoelectric device to provide the heating or cooling of the PCM reservoir while the vehicle is plugged in, while simultaneously opening a selective inlet and outlet path to the ambient air for the air necessary for operation of the thermoelectric device.
Once charged, however, the heat battery is used in a conventional, direct conduction or convection manner. That is, hot air from the cabin is blown directly over it to be cooled in the summer, or cold cabin air blown over it to be heated in the winter. As a consequence, a different PCM material with a melt temperature comparable to the very different heating comfort level temperature in the winter, or to the cooling comfort level temperature in the summer, would have to be used, and swapped out as the seasons changed. This is an inconvenience that a vehicle owner would be unlikely to tolerate.
Another proposal, disclosed in WO2013/088190, uses a single PCM reservoir, but in an internal combustion engine car, and with a very complex flow and control circuitry. The PCM reservoir has a melt temperature near, or just below, the cooling mode target temperature, and it is cooled by the “extra” compressor power available when the compressor is operating as the internal combustion engine is operating. Cabin air, in turn, is cooled by forced flow directly across a heat exchanger that carries a coolant cooled within the PCM reservoir to that temperature. In heating mode, extra heat from the internal combustion engine cooling system is used to elevate the temperature of what will already be likely melted PCM material in the reservoir. In the event that the internal combustion engine is switched off, as at a stop light, to save fuel, then an additional heating circuit can be switched in to draw heat by direct conduction or convection out of the previously heated PCM reservoir. In addition, an extra heat transfer circuit is provided, with an additional compressor and heat pump componentry, to draw additional heat indirectly out of the PCM reservoir when it has grown too cold to be used directly.
While the system does use a single PCM material, it is disclosed only in conjunction with an internal combustion engine, for which range extension is not an issue. Furthermore, the system is exceedingly complex and expensive, including three heat transfer loops, seven heat exchangers, two compressors and the components necessary for a vapor compression system, and approximately ten switchable flow valves. It seems unlikely that this level of complexity would ever be economical in terms of the level of thermodynamic advantage gained.